Conversion of carbonaceous materials, like biomass, biomass derived liquids, coal, char, coke, petroleum residue etc., into a gaseous fuel with a gasification agent like air, oxygen, and steam is called gasification. Generally, product of the gasification is a mixture mainly consisting of hydrogen and carbon monoxide called synthesis gas or syngas, and varying amounts of nitrogen, carbon dioxide, and hydrogen sulfide etc. During the gasification, ash is removed in the form of dry ash or molten slag during gasification. Also, various types of impurities from the syngas are removed through subsequent treatment steps. Syngas can be used for various purposes like production of chemicals such as methanol and hydrogen, and generation of electricity. Moreover, syngas can also be converted into synthetic fuels by using Fischer-Tropsch process.
Typically, the gasification reactions are endothermic and require combustion reactions to supplement energy requirement. Current approaches of applying gasifying processes such as biomass pyrolysis, moving bed gasification of coal, etc., in conventional gasification systems are targeted towards handling of specific type of feedstock only. Such systems also require extensive and cumbersome up-gradation of products such as pyrolysis oil, tar, and clean up of syngas.
Generally, the conventional gasification systems are operated at a high operating temperature, as a relatively low operating temperature leads to an excessive production of liquid tar along with the syngas. However, operation at such temperature leads to vaporization of metallic impurities and contaminants present within the feedstock. The vaporized impurities and contaminants affect the quality of syngas. Employment of gas cleaning means for removing such vaporized impurities from the finally produced syngas proves complex and adds to the cost.
Due to the high operating temperature, the ash is removed in a solid or molten form at high temperature from the gasifiers, thereby consuming a lot of useful energy and rendering the conventional gasification system energy-inefficient. In addition, removal of such molten slag following gasification at the high temperature is also a tedious task and leads to a substantial heat losses. As a result conventional gasification system requires higher supply of pure oxygen or air.